Recently, an ink-jet recording method has been applied in various fields of printing works such as photograph imaging, various types of printings, markings and a specific printing such as a color filter because it enables to form an image easily and at small cost.
As ink-jet inks used for the ink-jet recording method, there are various types of ink such as an aqueous ink containing water as a principal solvent, an oil-based ink principally containing a non-volatile solvent at room temperature and substantially containing no water, a non-aqueous ink principally containing a solvent volatile at room temperature and substantially containing no water, a hot-melt ink which is solid at room temperature and thermally melted for printing and an active light curable ink capable of curing by active rays such as light. They are selected in accordance with the use.
Besides, as a recording medium used for outdoor notice board which is required to have weather resistance for a long period, and for a printing material which is required to have an ability of contacting with a curved surface, recording mediums made of plastics such as polyvinyl chloride and polyethylene are used. Particularly, a medium made of soft polyvinyl chloride is used in various fields of use. The ink-jet recording method is applied as a method suitable for making small amount and diverse kinds of printing matters since plate making is not necessary and the time for finishing is short by this system, though there are many methods to print an image on a soft polyvinyl chloride medium.
Hitherto, a non-aqueous ink containing cyclohexanone as the principal solvent is used on the occasion of printing on soft polyvinyl chloride. For example, an ink-jet ink containing cyclohexanone is disclosed (cf. Patent Document 1). Cyclohexanone has high dissolving ability for soft polyvinyl chloride so that the pigment contained in the ink will enter into soft polyvinyl chloride. Therefore, high abrasion resistance and high glossiness of the printed matter can be obtained. However, cyclohexanone has relatively high toxicity and exhibits high vapor pressure. It has not only some problems of safety but also a defect that a local exhausting system is necessary when the ink-jet ink containing cyclohexanone is handled.
In contrast to that, non-aqueous ink containing no cyclohexanone is developed and marketed. For example, there are disclosed non-aqueous inks containing an organic solvent such as N-methylpyrrolidone or amide as a solvent which is capable of dissolving polyvinyl chloride in place of cyclohexanone causing the above problems (cf. Patent Documents 2 and 3). Moreover, there is disclosed a non-aqueous ink containing a fixing resin such as a vinyl chloride-vinyl acetate copolymer or an acrylic resin for improving the fastness of the image such as abrasion resistance (cf. Patent Documents 4 and 5). By these constitution, it can be obtained an ink-jet ink which is inhibited the odor to some extent and has the abrasion resistivity of image formed thereby on polyvinyl chloride medium. However, the above-mentioned ink will often cause problems of ejection from an ink-jet head, which will results in degradation of printing image. A current status is that there is not yet obtained a non-aqueous ink-jet ink which has resolved the problems of safety and odor, and fully provided with abrasion resistance, and excellent in ejection characteristics from an ink jet head to produce a good printing image.    Patent Document 1: Japanese translation of PCT international application No. 2002-526631    Patent Document 2: Unexamined Japanese Patent Application (hereinafter, refers to as JP-A) No. 2005-15672    Patent Document 3: JP-A No. 2005-60716    Patent Document 4: JP-A No. 2005-36199    Patent Document 5: WO 2004/007626